<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>rw6</title>
</head>
<body>
<style>

    .left{

        width: 50px;

        float: left;

        border:1px solid red;

    }

    .right{

        width: 200px;

        float: right;

        border:1px solid red;

    }

    .content{

        border:1px solid red;

    }

</style>

<div class="left">left</div>

<div class="right">right</div>

<div class="content">content</div>
</body>
</html>